1. Field of the Invention
The present invention relates to field emission election-emissive elements arranged in a matrix form, and to a display element employing such electron-emissive elements as the electron source for discharging the emission of light by irradiating electrons with a fluorescent material. More particularly, the present invention relates to an electron-emissive element in which the pitch of electron-emissive unit areas is minimized in structures and the electron-emissive unit areas and switching elements for selectively driving the same are stacked, and also to a display element minimizing the pixel pitch of the display area as a result of the use of such an electron-emissive element as the electron source.
2. Description of the Related Art
Japanese Patent Application Laid-open Publication No. H6-44927 discloses a field emission cathode (FEC), which is capable of static drive, with a high display density and good properties in circuits built with FECs. The structure comprises a plurality of control wirings and data wirings forming a matrix on a monocrystalline silicon (Si) substrate. As a result, there is formed a plurality of element areas in which the elect-on-emissive elements are arranged. In each element area, a circuit element is formed on a crystalline Si substrate, and a field emission element is formed as a drive unit area thereon. The circuit element has a transistor that is a switching element in which the drain is connected to the data wiring and the gate is connected to the control wiring, a capacitor that is a memory circuit for input signals, and a transistor that amplifies and applies the input signals to the field emission part. This results in good properties in the circuit elements built on monocrystalline Si substrates, and the density is higher because the field emission part is stacked on top. It is also held that static drive is possible because the circuit element has a capacitor.
In the field emission cathode having the matrix structure disclosed in the above referenced related application, circuit elements are provided to selectively drive the field emission elements formed in each of the element areas of the matrix as described above. FIGS. 9(a) and (b) show the structure of the circuitry and field emission components of the element areas in the field emission cathode having such a matrix structure. FIG. 9(a) is an elevational view and FIG. 9(b) is a schematic cross section and circuit diagram.
A drive circuit A shown in FIGS. 9(a) and (b) is formed on a monocrystalline substrate of silicon or the like, and has an N-channel field-effect transistor (FET) as a switching element connected to a matrix wiring (not shown) arranged on the same monocrystalline substrate. The FET source S is connected to a data wiring (not shown), the gate G is connected to a control wiring (not shown), and the drain D is connected to an underlay electrode 101 of the field emission part 100 described below.
The field emission part 100 shown in FIGS. 9(a) and (b) is formed by being stacked on a corresponding drive circuit A, with an insulation layer in between. That is, the underlay electrode 101 is formed on an insulation layer (not shown) covering the drive circuit A, and an insulation layer 102 such as silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), or the like is formed on the underlay electrode 101. Furthermore, a gate electrode 103 such as a niobium (Nb) layer is formed on the insulation layer 102. Holes 104 are formed in the gate electrode 103 and insulation layer 102, and conical emitters 105 consisting of molybdenum (Mo) (or titanium (Ti), tungsten (W), etc.) are formed on the underlay electrode 101 exposed in the holes 104. The drain of the FET is connected to the underlay electrode 101 of the field emission part 100.
In the field emission part 100 having such a drive circuit A, when the gate G of the FET in the drive circuit A is ON, data signals of a predetermined potential are applied to the emitter 105, and electrons are emitted. When the gate G is OFF, the emitter 105 is not connected to any specific potential, i.e., floating. The potential therefore gradually increases, ultimately, from the data signal potential such as 0 (V) to Vg-Vth (V) wherein Vg is the gate voltage, and Vth is the inherent emission threshold voltage of the emitter. Upon reaching the threshold voltage Vg-Vth, the electron emission from the emitter 105 stops.
Thus, because electrons continue to be emitted from the emitter 105 in the time it takes for the potential to increase from 0 (V) to Vg-Vth (V), unnecessary light leakage occurs in a display area which emits light through electron bombardment using display elements in which the electron source is the field emission part 100 exhibiting such electron emission behavior.
It is known that the output stage of a transistor can be structurally made into a drive circuit A′ with a complementary structure (C-MOS), as shown in FIG. 10, to overcome such problems through circuitry. When the input in this drive circuit A′ is low, the p-channel FET is turned ON, resulting in an emitter 105 potential of Vg-Vth (V). When the input is high, the N-channel FET is turned ON, resulting in an emitter 105 potential of GND. In either case, the emitter 105 potential is not floating. In circuits with this type of C-MOS structure, the P-type FET may also be replaced with a resistor. For static drive, a memory function may be introduced with the addition of a capacitor to the drive circuit.
However, attempts to solve existing problems through these types of structural circuit modifications result in a number of new problems. For example, when such electron-emissive elements are used as an electron source in display elements, the field emission part of the element areas in the display elements arranged in a matrix correspond to the pixels of the display part, but the field emission part arrangement pitch which determines the pixel pitch is governed by the size of the circuit elements. In other words, the pixel pitch can be made smaller by constructing smaller circuit elements in the element areas, but the circuit elements are actually quite large in structures capable of solving the floating problem described above while satisfactorily meeting the withstand voltage performance required of the circuit elements. For example, a FET with 40 V withstand voltage is about 15 μm square, and the C-MOS structure with two FETs described above cannot be made when the required pixel pitch (about 20 μm, for example) is taken into consideration. This is also true even if one of the two FETs is replaced with a resistor. Adding a capacitor to the drive circuit A′ will result in even larger circuit elements.